A program of research on the physiology of motivation is presented. Studies utilizing a variety of experimental methods to investigate the mechanisms regulating reinforcing brain mechanisms, sexual behavior, and ingestion are described. Experiments on reinforcing brain mechanisms will include: 1) analysis of anatomical basis of reinforcement of neural circuits involving lateral hypothalamus, frontal cortex and dorsomedial thalamic nucleus; 2) affect of simultaneous activation of reinforcement mechanism on memory; 3) attempt to produce more lasting changes in emotional reactivity by brain stimulation; 4) further analysis of anatomical basis and behavioral characteristics of stimulation-elicited behavior. Sexual behavior investigations will emphasize estrogen and progesterone action on central nervous system mechanisms; olfactory bulb input to limbic and hypothalamic structures and regulation of sexual behavior. Studies of regulation of ingestion will include: 1) regulation of body weight "set point" following manipulation at different ages; 2) taste preferences as a function of deviation from set-point; 3) use of a newly developed brain cooling system to produce reversible blockade of structures implicated in ingestion.